Piezoelectric device and its manufacturing method

ABSTRACT

A piezoelectric device comprising a first electrode film, a second electrode film, and a piezoelectric thin film enclosed by the first electrode film and second electrode film, in which the piezoelectric thin film is an oxide piezoelectric thin film having an oxygen deficiency amount of more than 0% and not more than 10% of the stoichiometric composition. The piezoelectric device composed of the piezoelectric thin film having such oxygen deficiency has a greater piezoelectric performance as compared with the oxide piezoelectric thin film in oxidized state of stoichiometric composition, and by manufacturing in such condition, the film forming speed is increased, so that the mass producibility can be improved.

FIELD OF THE INVENTION

[0001] The present invention relates to a piezoelectric device having a piezoelectric thin film, and its manufacturing method.

BACKGROUND OF THE INVENTION

[0002] Recently, piezoelectric thin films are processed into various piezoelectric devices depending on the purpose, are widely used as electronic components such as an actuator for deforming by applying a voltage, or a sensor for generating a voltage by deforming the device. For example, Japanese Laid-open Patent No. 2002-279742 discloses a technology of fine control of head position in a magnetic disk by using a piezoelectric device. This is because the recording density of magnetic disk is increased and the area of recording region of one bit is decreased, and it is difficult to obtain a sufficient precision by positioning of the head using the conventional voice coil motor only. Accordingly, in addition to positioning by the voice coilmotor, it has been considered to compose a two-stage actuator for positioning at high precision in a very small region by a piezoelectric device. A piezoelectric device unit used for this purpose composed of a pair of piezoelectric devices, which are disposed so that one is contracted when other is expanded, and therefore the head provided at the leading end can be moved finely at high precision on the disk surface.

[0003] Such piezoelectric device is generally manufactured in the following manner. A substrate is, for example, a magnesium oxide single crystal substrate (MgO substrate). On this MgO substrate, a platinum film (Pt film) oriented by (100) is formed. On this Pt film, a lead zirconate titanate (PZT) thin film oriented by (001) is formed. Further, an electrode thin film is formed on the PZT thin film, and these thin films are processed into specified shape by photolithography and etching. Finally, by removing the MgO substrate by etching or other process, a piezoelectric device is fabricated.

[0004] For forming a PZT thin film, generally, a sputtering method is employed, and its substrate temperature is 550 to 650° C. By sputtering at such high temperature, lead (Pb) is evaporated again from the PZT thin film in sputtering process, and the finally fabricated PZT thin film is deviated from the stoichiometric composition by decrease of Pb composition. To obtain the PZT thin film of stoichiometric composition, Takayama et al. attempted to compensate the Pb component in the PZT thin film by composing the target for sputtering by containing Pb by about 20% in excess, and forming the film by using this target (J. Appl. Phys. 65 (4), 1666, 1989).

[0005] However, to obtain the PZT thin film of stoichiometric composition by using the target containing Pb in excess, it is required to add oxygen gas to inert gas as discharge gas for sputtering, and form the film by sputtering in a condition of relatively high pressure. In such condition, the film forming speed cannot be increased. When used as piezoelectric device, the PZT thin film is required to form about 1 μm to 10 μm in thickness, and the mass productivity is extremely lowered at slow film forming speed.

[0006] Japanese Laid-open Patent No. H6-49638 discloses a technology of sputtering at a relatively low discharge gas pressure in the vacuum apparatus for increasing the film forming speed when forming a PZT thin film for use in semiconductor memory. When the discharge gas pressure is low, the Pb component in the formed film is likely to decrease, and to fabricate a PZT thin film of stoichiometric composition, a target of excessive Pb composition is used depending on the discharge gas pressure.

[0007] On the other hand, Japanese Patent Publication No. 3341357 discloses a technology of increasing the piezoelectric constant d₃₁by containing an excessive Pb in the thin film fabricated for improving the piezoelectric characteristics of the PZT thin film more than in the stoichiometric composition, and forming the rhombohedral crystal structure.

[0008] In the first prior art and second prior art, however, both are intended to fabricate PZT thin film of stoichiometric composition, and it is required to form the film by sputtering in a discharge gas of relatively high oxygen partial pressure. In the PZT thin film formed at such high oxygen partial pressure, the piezoelectric constant d₃₁ is generally small, and the film forming speed in sputtering cannot be increased. Hence, good piezoelectric characteristics are not obtained, and the mass producibility is not improved.

[0009] In the third prior art, the Pb amount in the PZT thin film is in excess of the summed amount of titanium (Ti) and zirconium (Zr), but the ratio of oxygen (O) and Pb in the PZT thin film is increased at a same rate, and oxygen deficiency does not take place. Accordingly, when forming the film, oxygen must be added more, and sputtering must be done in the condition of high discharge gas pressure, and the film forming speed is not increased. Hence, mass productivity is not improved.

SUMMARY OF THE INVENTION

[0010] The invention is based on the finding that an appropriate oxygen deficiency amount for oxide piezoelectric thin film contributes to improvement of piezoelectric constant d₃₁ and realization of piezoelectric device of favorable piezoelectric characteristics, and hence presents a piezoelectric device of excellent piezoelectric characteristics, increased film forming speed, and enhanced mass productivity, and a method of manufacturing the same.

[0011] To solve the problems, the piezoelectric device of the invention comprises:

[0012] a first electrode film, a second electrode film, and a piezoelectric thin film enclosed by the first electrode film and the second electrode film,

[0013] in which the piezoelectric thin film is an oxide piezoelectric thin film having an oxygen deficiency amount of more than 0% and not more than 10% of the stoichiometric composition.

[0014] By using the oxide piezoelectric thin film having such oxygen deficiency, a piezoelectric device having a more favorable piezoelectric characteristic than before can be obtained, and the film can be formed at high speed, and hence the characteristics of the piezoelectric device are enhanced, and improvement of mass productivity is realized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of piezoelectric device in an exemplary embodiment of the invention.

[0016]FIG. 2 is a sectional view of principal process of manufacturing method of piezoelectric device in the exemplary embodiment.

[0017]FIG. 3 is a diagram showing the dependence of the crystal orientation degree and the displacement of the piezoelectric device 10 formed by using the target of Y=0.25 composition on the oxygen partial pressure in the sputtering.

[0018]FIG. 4 is a diagram showing the dependence of a ratio of the oxygen deficiency amount (oxygen deficiency ratio) (Y−Z)/(Y+3) and the displacement of the piezoelectric device on the oxygen partial pressure in the sputtering.

[0019]FIG. 5 is a diagram showing the relationship between the oxygen deficiency ratio (Y−Z)/(Y+3) and the displacement of the piezoelectric device in the exemplary embodiment.

[0020]FIG. 6 is a diagram showing the relationship between the displacement of the piezoelectric device manufactured by using a target with different composition (Y=0, Y=0.25, and Y=1) and oxygen partial pressure in the sputtering.

[0021]FIG. 7 is a diagram showing an example of using the piezoelectric device in the exemplary embodiment for positioning the magnetic head of a magnetic disk device.

[0022]FIG. 8A is a plan view showing the shape near the piezoelectric device of the magnetic disk device in the exemplary embodiment.

[0023]FIG. 8B is a sectional view along line X-X in FIG. 8A.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0024] An exemplary embodiment of the invention is described below while referring to the accompanying drawings. In the following drawings, same elements are identified with same reference numerals, and duplicate explanation may be omitted.

First Exemplary Embodiment

[0025]FIG. 1 is a perspective view of piezoelectric device in a first exemplary embodiment of the invention. FIG. 1 also shows a driving power source 5 for driving this piezoelectric device 10.

[0026] The piezoelectric device 10 comprises a first electrode film 1, an oxide piezoelectric thin film 2 formed on the first electrode film 1, and a second electrode film 3 formed on the oxide piezoelectric thin film 2. The first electrode film 1, oxide piezoelectric thin film 2, and second electrode film 3 are formed by thin film deposition technology such as sputtering, and processed in a nearly box shape as shown in FIG. 1 by photolithography and etching process.

[0027] The piezoelectric device 10 measures, for example, about 2 mm in the expanding direction of the piezoelectric element, that is, in length direction (direction B in the drawing), about 0.5 mm in width direction, and about 3 μm in thickness. For use as piezoelectric device 10, the oxide piezoelectric thin film 2 must undergo initial polarization, and in this exemplary embodiment, as shown in FIG. 1, the direction of polarization is direction of arrow A. The polarization vector is not always required to be vertical to the film surface, and in the case of the oblique polarization vector to the surface, its vertical component may be taken. That is, the entire domain of the oxide piezoelectric thin film 2 is not required to be polarized in the direction of film thickness.

[0028] If spontaneous polarization occurs naturally right after forming the film, such spontaneous polarization may be utilized. The shape of the piezoelectric device 10 is not limited to a box shape. For example, depending on the shape of an apparatus to be used with, its cross section maybe formed in a trapezoidal, triangular or other shape.

[0029] The driving power source 5 is used for applying a specified voltage to the piezoelectric device 10, and the voltage is applied to oxide piezoelectric thin film 2 through the first electrode film 1 and second electrode film 3, and the oxide piezoelectric thin film 2 is expanded or contracted by this voltage.

[0030] In this structure, the piezoelectric device 10 can be expanded and contracted in the direction of arrow B depending on the voltage of the driving power source 5. In this exemplary embodiment, this expanding and contracting motion is used as the actuator. That is, fixing one end and setting other end substantially as a free end, the object to be controlled is fixed to this free end, and hence the object can be positioned precisely. The displacement per voltage depends on the piezoelectric constant d₃₁ which is one of the indices of piezoelectric properties, and the greater this value, the larger is the displacement of the device.

[0031] In the invention, the oxygen deficiency amount in the film of the oxide piezoelectric thin film 2 is controlled in a range of more than 0% to not more than 10%, preferably more than 2% to 7% or less, or more preferably more than 2% to 5% or less. The present inventor discovered that the piezoelectric device formed by the oxide piezoelectric thin film having such oxygen deficiency amount is a larger piezoelectric characteristic than the piezoelectric device formed by the oxide piezoelectric thin film in oxidized state of stoichiometric composition. Further, by manufacturing the oxide piezoelectric thin film in such condition, the film forming speed is increased and the mass productivity is improved.

[0032] By defining the oxygen deficiency amount more than 0% and not more than 10%, the piezoelectric constant d₃₁ can be increased, and hence the displacement of the piezoelectric device can be increased. For example, when using the PZT thin film expressed in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z), the oxygen deficiency ratio (Y−Z)/(Y+3) is set at more than 0 and not more than 0.1 (that is, 10%).

[0033] Moreover, when the oxygen deficiency amount is set at more than 2% and 7% or less, fluctuations of the crystal orientation degree can be suppressed, and if the oxygen deficiency amount varies, variation of the displacement of the piezoelectric device can be suppressed relatively small. Hence, the manufacturing yield is improved. Further by defining the oxygen deficiency amount in a range of more than 2% to 5% or less, fluctuations of displacement of the piezoelectric device can be further suppressed. As a result, the manufacturing yield is further improved.

[0034] Preferably, the oxide piezoelectric thin film should be having the crystal orientation defined so that the axis of polarization may coincide with the film thickness direction. For example, a tetragonal PZT thin film should be oriented in (001) direction, and a rhombohedral PZT thin film, in (111) direction.

[0035] As an example of forming an oxide piezoelectric thin film expressed in general formula A_(1+Y)BO_(3+Z)(where A and B represent elements) and 70% or more in the crystal orientation degree of an azimuth parallel to the axis of its polarization, a specific manufacturing method is explained below about a PZT thin film expressed in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z) by sputtering, together with results of measurement of piezoelectric characteristics.

[0036]FIG. 2A to FIG. 2D are sectional views showing the principal process of manufacturing method of the piezoelectric device 10 in the exemplary embodiment.

[0037] The substrate is an MgO substrate of (100) azimuth. On this MgO substrate 15, a Pt film 1 was formed as a first electrode film in a film thickness of 100 nm and in (100) orientation, by sputtering, at substrate temperature of 500° C., using argon (Ar) gas, at a discharge gas pressure of 0.5 Pa.

[0038] On the Pt film 1, a PZT thin film 2 was formed as the oxide piezoelectric thin film in a film thickness of 5 μm. FIG. 2A is a sectional view showing a state of forming the PZT thin film 2. At this time, when the sputtering target was expressed in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z) (where 0<X<1), the sputtering target with a composition of X=0.58 and Y=0.25 was used. At this time, the value of Z was same as the value of Y.

[0039] Discharge gas pressure in sputtering was 0.5 Pa, and substrate temperature was 600° C. At this time, the composition of discharge gas was a mixed gas of Ar gas and oxygen (O₂) gas, and the rate of O₂ gas in the discharge gas was varied in the condition of 0.5% to 50% of total gas. Including the forming process of PZT thin film 2, the composition of discharge gas in the discharge space between the target and substrate was measured by a mass filter. The prepared PZT thin film 2 was measured by electron probe microanalysis (EPMA) to determine the film composition and analyzed by X-ray diffraction to evaluate the crystallization.

[0040] In succession, as a second electrode film, a Pt film 3 was formed on the PZT thin film 2 by sputtering, using Ar gas, at discharge gas pressure of 0.5 Pa and at ordinary temperature. FIG. 2B is a sectional view showing a state of forming the Pt film 3. In the PZT thin film 2 fabricated in this condition, spontaneous polarization in upward direction of the substrate surface was confirmed naturally without particularly applying electric field to induce polarization.

[0041] Next, as shown in FIG. 2C, by photolithography and etching process on the MgO substrate 15, a specified piezoelectric device shape was formed. The shape is, as shown in FIG. 1, 2 mm in longitudinal direction and 0.5 mm in width direction.

[0042] After thus processing into a specified shape, as shown in FIG. 2D, the MgO substrate 15 was removed by etching, and the piezoelectric device 10 in the shape as shown in FIG. 1 was obtained.

[0043] To the fabricated piezoelectric element 10, a driving power source 5 was connected as shown in FIG. 1, and displacement in direction of arrow B was measured. A voltage of 10 V was applied. Displacement was measured as the amount of displacement in direction of arrow B by using a laser Doppler vibrometer, when voltage of 10 V is applied.

[0044]FIG. 3 shows the result of the dependence of the crystal orientation degree and the displacement of piezoelectric device 10 formed by using the target of Y=0.25 composition on the oxygen partial pressure in the sputtering. The axis of abscissa denotes the oxygen partial pressure in percentage to the total pressure, and the axes of ordinates represents the displacement at the left side and the crystal orientation degree at the right side.

[0045] Crystal orientation degree of PZT thin film 2 was determined by X-ray diffraction apparatus. In X-ray diffraction, θ-2θ scan was done by using Cu-Kα X-ray source. Angle range of 2θ was 20 to 40 degrees. In the tetragonal PZT thin film 2, since the polarization is in (001) direction, the crystal orientation was determined by the peak intensity ratio (001)/Σ(hk1) of X-ray diffraction. A material having polarization in (001) direction is determined by (001)/σ(hk1),and a material having polarization in (111) direction is determined by (111)/σ(hk1). Herein, σ(hk1) is the sum of reflection peak intensity derived from PZT in the case of setting the upper limit and lower limit of 2θ in a minimum range capable of measuring all(hk1) reflection except for (000) reflection, where h, k and l are 0 or 1, in θ-2θ scan using Cu-Kα X-ray source. Hereinafter, the crystal orientation degree may be simply called orientation degree.

[0046] As clear from FIG. 3, the orientation degree drops at the oxygen partial pressure of 2% or less, but even at oxygen partial pressure of 0.5%, the orientation degree is 60%. When the oxygen partial pressure reaches 50%, the orientation degree drops suddenly, but the orientation degree is 65% even in this case. In the range of oxygen partial pressure of 0.5% to 10%, for example, at oxygen partial pressure of 1.5%, the orientation degree is 95%, and as the oxygen partial pressure is further increased, the orientation degree gradually increases, and at oxygen partial pressure of 10%, the orientation degree is 100%. In the range of oxygen partial pressure of 10% to 30%, the orientation degree is 100%, and at oxygen partial pressure of 40%, the orientation degree is 96%, and at a higher oxygen partial pressure, the orientation degree falls suddenly.

[0047] On the other hand, the displacement increases sharply as the oxygen partial pressure increases from 0.5% to 2%. Exceeding 2%, however, the displacement decreases. The rate of decrease differs around the oxygen partial pressure of about 10%, and a point of inflection is noted.

[0048]FIG. 4 shows the result of the dependence of the oxygen deficiency ratio(Y−Z)/(Y+3) and the displacement of the piezoelectric device 10 on the oxygen partial pressure in the sputtering, similarly using the target of Y=0.25 composition. The axis of abscissa denotes the oxygen partial pressure in percentage to the total pressure, and the axes of ordinates represents the displacement at the left side and the oxygen deficiency ratio (Y−Z)/(Y+3) at the right side. FIG. 5 is a diagram showing the relation between the oxygen deficiency ratio (Y−Z)/(Y+3) and displacement.

[0049] The method of determining the oxygen deficiency ratio (Y−Z)/(Y+3) is explained below. First, the composition of ferroelectric thin film necessary for determining the oxygen deficiency ratio was measured by EPMA as mentioned above. In this method of analysis, a very narrow reduced electron beam flux is emitted to the sample surface, and the wavelength and intensity of the characteristic X-ray radiated from the spot are measured by X-ray spectroscope, and the composition of the sample is determined.

[0050] The PZT thin film was quantitatively analyzed as follows. Using a standard sample with known concentration of elements Pb, Zr, Ti and O, the X-ray intensity is measured in the first place. For example, Pb is explained. Suppose the Pb concentration of standard sample to be W_(pbstd), and X-ray intensity of this sample to be I_(pbstd). When a PZT thin film of unknown concentration is measured, suppose the X-ray intensity of Pb to be I_(Pb). By linear approximation of these data, the Pb concentration W_(pb) of the PZT thin film of unknown concentration is determined in the following formula.

W _(Pb) =W _(Pbstd) ×I _(Pb/) I _(Pbstd)

[0051] where I_(Pb) and I_(Pbstd) are X-ray intensity per unit current after dead time correction and background correction.

[0052] By similar method, concentrations of Zr, Ti and O are determined as W_(Zr), W_(Ti) and W_(O).

[0053] Next, the ZAF correction coefficient is calculated. Z is the atomic number correction, which is determined by calculating the numerical value of Duncumb-Reed by the method of least squares. A is the absorption correction, which is calculated by the formula of Philibert. F is the fluorescence correction, which is calculated by the formula of Reed. From the normalized values of W_(Pb), W_(Zr), W_(Ti), and W_(O), values of Z, A and F of the first ZAF correction coefficient of each element are calculated, and by multiplying them, a corrected concentration is obtained. Using the obtained values of concentration, the ZAF correction coefficient is calculated again. By using this correction coefficient, a further corrected concentration is determined. Thus, by repeating until the calculation error is 0.001%, a quantitative value is obtained.

[0054] The apparatus used in analysis is wavelength dispersion type EPMA (JXA-8900R of JEOL Ltd.). The sample is processed in a square shape of about 5 mm in size. It is adhered to the sample stand by carbon paste to achieve conduction, and carbon coating is also applied on the surface.

[0055] In actual measurement, first, to measure film thickness and check for impurities, the sample is inspected by total qualitative analysis. At the same time, it is checked if the electron beam has invaded down to the matrix. Next, PZT of the standard sample is measured. Reading the value of the standard sample, the sample is analyzed quantitatively. The condition of analysis at this time is acceleration voltage of 15 kV, irradiation current of 70 mA, and beam diameter of 10 μm. After checking for abnormality of measurement, if measured normally, the measured data is normalized, and the result of measurement is obtained. In this measuring method, the quantitative values of Pb, Zr, Ti, and O are obtained.

[0056] Oxygen deficiency ratio (Y−Z)/(Y+3) is defined as the ratio of oxygen deficiency amount in the PZT thin film 2 supposing Pb to be valence of two and Zr and Ti as valence of four. In other words, if oxidization of Pb completely takes place stoichiometrically, the oxygen (O) amount at this time is same as that of Pb, that is, Y+1, and similarly if oxidization of Zr completely takes place stoichiometrically, the oxygen (0) amount at this time is two times that of Zr, that is, 2X, and if oxidization of Ti takes place similarly, the oxygen (O) amount is two times that of Ti, that is, 2(1−X). Therefore, in the state of stoichiometric composition, the total oxygen amount is (Y+1)+2X+2(1−X)=(Y+3).

[0057] On the other hand, the actual oxygen amount of the fabricated PZT thin film 2 is (3+Z), and the oxygen shortage is (Y+3)−(3+Z)=(Y−Z). Since the total oxygen amount of stoichiometric composition is (Y+3), the rate of oxygen deficiency amount is the ratio of the two, that is, (Y−Z)/(Y+3). Thus, (Y−Z)/(Y+3) represents the oxygen deficiency ratio. The values of X, Y and Z are easily obtained by calculating on the basis of values of W_(Pb), W_(Zr), W_(Ti) and W_(O) because they are determined from the quantitative analysis results by EPMA.

[0058] As shown in FIG. 4, at the oxygen partial pressure of 1% or less, it is found that the oxygen deficiency ratio (Y−Z)/(Y+3) increases suddenly along with decline of oxygen partial pressure. That is, at the oxygen partial pressure of 1% or less, it is known that much oxygen deficiency occurs in the PZT thin film 2. As the oxygen partial pressure exceeds 1%, the oxygen deficiency ratio gradually becomes smaller, and at the oxygen partial pressure of 10%, the oxygen deficiency ratio is 0.2% (0.002), and at a higher oxygen partial pressure, a PZT thin film of stoichiometric composition is obtained.

[0059] Further as known from FIG. 4, from the oxygen partial pressure of 10% where the oxygen deficiency ratio is 0.2% to the oxygen partial pressure of 2% where the oxygen deficiency ratio is 5% (0.05), there is an almost linearly increasing tendency of displacement along with the increase of the oxygen deficiency ratio. However, when the oxygen deficiency ratio exceeds 5% (0.05), the displacement becomes smaller to the contrary, and in this region there is no correlation with the oxygen deficiency ratio. The cause is the decline of the orientation degree as shown in FIG. 3.

[0060]FIG. 5 is a diagram showing the relation between the oxygen deficiency ratio (Y−Z)/(Y+3) and displacement. The displacement shows the maximum value at the oxygen deficiency ratio of about 5% (0.05). When the oxygen deficiency ratio is smaller than 5%, the displacement decreases gradually. On the other hand, at the oxygen deficiency ratio of over 5%, it decreases similarly, but at the oxygen deficiency ratio of around 10%, it seems there is a point of inflection in the displacement.

[0061] Summing up these results, to increase the displacement of the piezoelectric device 10, it has been found effective to cause a certain oxygen deficiency in the PZT thin film 2. The upper limit of the oxygen deficiency ratio is 0.1 when the orientation degree of PZT thin film 2 is 70% or more. This is because it is known from FIG. 4 that the oxygen deficiency ratio of 0.1 or less is required in order to assure a greater displacement than in the case free from oxygen deficiency at the orientation degree of 100%. At this time, the oxygen partial pressure is required to be in a range of more than 1% and not more than 10%.

[0062] Further, when the oxygen deficiency ratio is in a range of 2% (0.02) to 7% (0.07), as clear from FIG. 5, the range covers the peak value of the displacement, and if the oxygen deficiency fluctuates, variations of the displacement can be suppressed relatively small. Hence, the manufacturing yield can be improved. Moreover, at the oxygen deficiency ratio of 2% or more and 5% or less, variations of the displacement may be suppressed further for the oxygen deficiency ratio. Hence, the manufacturing yield can be further improved.

[0063] In the oxygen deficiency ratio range of 2% to 7%, the oxygen partial pressure should be set in a range of 1.5% or more and smaller than 5%.

[0064]FIG. 6 shows the relation between the oxygen partial pressure in the discharge gas when forming the film and the displacement of the piezoelectric device 10 formed by the PZT thin film 2, which is fabricated respectively by using three types of target(Y=0, Y=0.25, and Y=1) of which composition is expressed in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X)O) _(3+Z) (where 0<x<1). But, the composition of X=0.58 is constant.

[0065] Using the target of Y=0, the displacement has its peak in a range of oxygen partial pressure of 10% to 20%, and the displacement is small on the whole. Because of the target of Y=0, the PZT thin film formed by using this target is in Pb shortage state.

[0066] Using the target of Y=1, the displacement has a peak locally at the oxygen partial pressure of around 1%.

[0067] On the other hand, using the target of Y=0.25, the range of obtaining a large displacement is wider, and the PZT thin film 2 can be manufactured at a higher yield.

[0068] Incidentally, as clear from FIG. 6, as the value of “Y” showing the Pb composition in the target becomes larger than 0, the oxygen partial pressure showing the peak of displacement tends to be smaller. Although not shown in the diagram, by using the target varied the value of Y further, the relation with the displacement was studied. As a result, in a range of 0<Y<1, by forming the film in a range of oxygen partial pressure of 1% to 10%, it has been found that the piezoelectric characteristic is favorable while the mass productivity and yield are improved. This oxygen partial pressure may be achieved by controlling the ratio of the feeding Ar gas and O₂ gas while analyzing the discharge gas by mass filter during sputtering. Or, in the case of the target of Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z)and if Z is nearly 0, a similar piezoelectric thin film is obtained by feeding the discharge gas by setting the flow rate ratio of Ar and O₂ for achieving the range specified above.

[0069] In this exemplary embodiment, when expressed in general formula Pb_(1+Y) (Zr_(X)Ti_(1−X))O_(3+Z) (where 0<X<1), the target of X=0.58 constant and Z of the same value as Y was used. However, the value of Z in the oxygen composition of the target is not limited to the same value as Y in the Pb composition, but each value may be set individually. That is, as far as in a range of −3≦Z≦Y, by setting the oxygen content in the discharge gas in sputtering in the above range and properly controlling the film forming speed, a oxide piezoelectric thin film having favorable piezoelectric characteristic can be formed.

[0070] In this exemplary embodiment, the MgO substrate of (100) azimuth was used as the substrate, but the invention is not limited to this example. For example, other substrates may be used, such as single crystal silicon substrate, single crystal strontium titanate substrate, sapphire substrate, sintered alumina substrate, and zirconia substrate. If spontaneous polarization does not take place by using such substrates, polarization may be processed after forming the oxide piezoelectric thin film.

[0071] Also in the exemplary embodiment, the Pt film was used as the first electrode film, but the invention is not limited to this example alone. Other conductive materials may be used such as gold (Au), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), or their oxides which have electrical conductivity.

[0072] Also in the exemplary embodiment, moreover, the Pt film was used as the second electrode film, but the invention is not limited to this example alone. For example, same materials as for the first electrode film may be used. Further, metal materials such as aluminum (Al), copper (Cu), nickel (Ni) and others may be used without any limitation.

[0073] In the exemplary embodiment, the piezoelectric device is manufactured by photolithography and etching process, but the invention is not limited to such process. For example, by using a mask, a specified shape may be formed by sputtering or vapor deposition.

Second Exemplary Embodiment

[0074] This exemplary embodiment refers to a case of manufacturing an actuator composed of a piezoelectric device fabricated in the method explained in the first exemplary embodiment, and using this actuator in positioning of magnetic disk of magnetic disk drive device. FIG. 7 is a schematic diagram of device configuration using the piezoelectric device in this exemplary embodiment for positioning the magnetic head of a magnetic disk drive device. This magnetic disk drive device is characterized by a two-stage actuator configuration adding the actuator composed of the piezoelectric device of the invention to the actuator composed of a conventional voice coil motor. A head support mechanism 100 comprises a suspension 104 of a relatively low rigidity, a plate spring 105, an arm 106 of a relatively high rigidity, a flexure 103, a slider 102 mounted on this flexure 103 on the side facing a disk 200, a head (not shown) mounted on this slider 102, and a piezoelectric device 108 adhered and fixed on the flexure 103.

[0075] The suspension 104 is designed at a relatively low rigidity, and its other end forms a plate spring 105, and this plate spring 105 is fixed to an arm 106. A voice coil motor is composed of a voice coil 112 attached to the arm 106 and a magnet not shown in the drawing. A head support mechanism 100 can be rotated by this voice coil motor in a specified angle range in a direction parallel to the plane of a disk 200.

[0076] A piezoelectric device 108 is driven for positioning the head mounted on the slider 102 at high precision on a specified track position of the disk 200.That is, this head support mechanism 100 has a two-stage actuator structure of positioning roughly by the voice coil motor, and adjusting finely by the piezoelectric device 108.

[0077] The operation of this magnetic disk drive device is explained. The disk 200 is rotated at a specified speed by rotary driving means 220.In recording and reproducing operation of the magnetic disk drive device, the slider 102 flies by a specified flying height by the balance of the buoyancy of the air stream caused by rotation of the disk 200 and the thrusting force of forcing the slider 102 to the disk 200 side, and the head records and reproduces in this specific flying height. By recording and reproducing in such flying height, to position the head at the specified track position, the arm 106 is rotated by the voice coil motor about the bearing 110.In a conventional magnetic disk drive device, positioning is attempted by the voice coil motor only, but in the magnetic disk drive device of the present exemplary embodiment, positioning of higher precision is achieved by the piezoelectric device 108.

[0078]FIG. 8A and FIG. 8B show the shape near the piezoelectric device 108. FIG. 8A is a plan view, and FIG. 8B is a sectional view along line X-X in FIG. 8A. A pair of piezoelectric devices 108A, 108B are adhered and fixed on the flexure 103 by way of an adhesive layer 107 at symmetrical positions to the center line Y-Y in the longitudinal direction of the suspension. The piezoelectric devices 108A, 108B are symmetrical to the line Y-Y, and are identical in sectional structure. That is, the piezoelectric devices 108A, 108B are formed by a first electrode film 1081 and a second electrode film 1083 so as to enclose a PZT thin film 1082. On the surface of the piezoelectric devices 108A, 108B, further, an insulating protective resin film may be formed. The first electrode film 1081 and second electrode film 1083 of the piezoelectric devices 108A, 108B are connected by means of an electrode pad 103A of the flexure 103 and a wire lead 109. From the electrode pad 103A, a piezoelectric electrode wiring 103B to be connected to a control unit (not shown) of a magnetic disk apparatus is formed on the flexure 103. To connect the head mounted on the slider 102 and the control unit (not shown) of the magnetic disk apparatus, a head electrode wiring 103C is formed on the flexure 103 in the middle of the pair of piezoelectric devices 108A, 108B.

[0079] In the piezoelectric device 108 in this head support mechanism 100, a voltage 10 V was applied, and the displacement of the head (not shown) was measured. As a result, in the case of the PZT thin film of which oxygen deficiency ratio is 0<(Y−Z)/(Y+3)≦0.1, the generated displacement was more than 2 times as compared with the piezoelectric device of conventional PZT thin film. Therefore, as compared with the conventional piezoelectric device, a fine positioning is possible in a wider range, and a magnetic disk apparatus of a higher recording density is realized.

[0080] In the piezoelectric devices 108A, 108B shown in FIG. 8A and FIG. 8B, the PZT thin film 1082 is enclosed by the first electrode film 1081 and second electrode film 1083, and there is only one layer of PZT thin film 1082, but plural layers of PZT thin film may be laminated by gluing the films together with adhesive or the like. By laminating, a greater displacement driving force may be obtained.

[0081] In the PZT thin film of this exemplary embodiment, the crystal structure is a tetragonal system of (001) orientation, and in the tetragonal PZT, since the polarization is in (001) direction, orientation in (001) is advantageous for piezoelectric characteristic. In the case of PZT thin film of rhombohedral system, since the polarization is in (111) direction, the orientation in (111) is advantageous for piezoelectric characteristic.

[0082] In this exemplary embodiment, in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z), the case of X=0.58 is explained, but the invention is not limited to this example alone. In the PZT, the crystal structure depends on the composition of X, and the composition around the boundary of tetragonal system and rhombohedral system is called MPB (morphotropic phase boundary) composition, and it is known that the piezoelectric performance is higher. By using the composition in this vicinity, not limited to X=0.58, a piezoelectric device of high piezoelectric characteristic may be obtained. The value of X in the boundary of tetragonal system and rhombohedral system depends on the film forming method, amount of additives and others, and it may be adjusted properly.

[0083] In the exemplary embodiment, PZT is explained as the material for piezoelectric thin film, but additive elements may be added as required and the material characteristic may be adjusted. In such a case, the oxygen deficiency amount may be calculated in consideration of the amount of additives and the valence. Additive elements and valence are, for example, as follows. Group 1 elements have a valence of one, and group 2 elements, for example, Mn, Ni, Cu, Zn, Sm, Eu, and Yb have a valence of two, Sc, Y, Cr, B, Al, Ga, In, Sb, Bi, La, Nd, Pm, Gd, Dy, Ho, Er, Tm, and Lu have a valence of three, and Hf, Ir, Si, Ge, Sn, Ce, Pr, and Tb have a valence of four.

[0084] In the exemplary embodiment, a PZT thin film was directly formed on the Pt film, but to improve the crystallinity and crystal orientation of the PZT thin film, a base film may be formed on the Pt film, and a PZT thin film may be formed thereon.

[0085] In the exemplary embodiment, heat treatment is not performed after forming the film, but heat treatment may be also performed for improving the crystallinity and crystal orientation of the PZT thin film.

[0086] Films are formed by sputtering in the exemplary embodiment, but not limited to sputtering, a PZT thin film formed by laser ablation is also confirmed to be enhance in piezoelectric performance by forming a film having oxygen deficiency. The invention is not limited to PZT thin film, but the effects of the invention are obtained in any other oxide piezoelectric thin film.

[0087] In the piezoelectric device of the invention, the crystal structure of piezoelectric thin film may have a perovskite tetragonal system, and the azimuth parallel to the axis of polarization maybe (001) plane azimuth, or the crystal structure of piezoelectric thin film may have a perovskite rhombohedral system, and the azimuth parallel to the axis of polarization may be (111) plane azimuth. Thus, the piezoelectric device manufactured by using tetragonal PZT thin film or rhombohedral PZT thin film as piezoelectric material comes to have a great piezoelectric performance.

[0088] In the piezoelectric device of the invention, part of Pb in general formula Pb_(1+Y) (Zr_(X)Ti_(1−X))O_(3+Z) (where 0<X<1) maybe replaced by at least one element selected from the group consisting of group 2 elements of manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), samarium (Sm), europium (Eu), and ytterbium (Yb). In the composite oxide piezoelectric thin film adding one or plural elements thereof, the piezoelectric performance may be further improved by defining the oxygen deficiency in range of more than 0% to not more than 10%.

[0089] Further, in the piezoelectric device of the invention, part of at least Ti or Zr in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z) (where O<X<1) may be replaced by at least one element selected from the group consisting of hafnium (Hf), iridium (Ir), silicon (Si), germanium (Ge), tin (Sn), cerium (Ce), praseodymium (Pr), and terbium (Tb). In the composite oxide piezoelectric thin film replacing at least Ti or Zr with one or plural elements thereof, the piezoelectric performance may be further improved by defining the oxygen deficiency in range of more than 0% to not more than 10%.

[0090] Further, in the piezoelectric device of the invention, part of at least Pb, Ti or Zr in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z) (where O<X<1) may be replaced by at least one element selected from the group consisting of group 1 elements of valence of one, that is, scandium (Sc), yttrium (Y), chromium (Cr), boron (B), aluminum (Al), gallium (Ga), indium (In), antimony (Sb), bismuth (Bi), lanthanum (La), neodymium (Nd), promethium (Pm), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and lutetium (Lu). In the composite oxide piezoelectric thin film replacing at least Pb, Ti or Zr with one or plural elements thereof, the piezoelectric performance may be further improved by defining the oxygen deficiency in range of more than 0% to not more than 10%.

[0091] Also in the first exemplary embodiment and second exemplary embodiment, the method of manufacturing the piezoelectric thin film by sputtering is explained, but the invention is not limited to this example alone. For example, on the first electrode film, an oxide piezoelectric thin film expressed in general formula A_(1+Y)BO_(3+Z) where A and B represent elements) and 70% or more in the crystal orientation degree of an azimuth parallel to the axis of its polarization may be formed by laser ablation method. By forming the film in discharge gas atmosphere with the oxygen partial pressure control at high precision in the vacuum apparatus during film forming process, crystal growth of oxide piezoelectric thin film is realized while precisely controlling the oxygen deficiency amount, and distribution of oxygen deficiency in the film may be made homogeneous.

[0092] By contrast, for example, when forming a piezoelectric element by powder sintering method, although oxygen deficiency can be formed by baking in low oxygen atmosphere, but in this case the oxygen deficiency is likely to be localized, and the reliability is lowered. In the case of chemical vapor deposition (CVD) method, unlike the sputtering method or laser ablation method, since the film is formed by oxidation and decomposition of reaction gas, it is relatively difficult to form a piezoelectric thin film of excellent piezoelectric characteristic at low oxygen partial pressure.

[0093] On the other hand, in the oxide piezoelectric thin film formed by sputtering method or laser ablation method, a specified oxygen deficiency is homogeneously present in the film, and a piezoelectric thin film of large piezoelectric performance and high reliability is obtained. By sputtering in a state of the oxygen partial pressure exceeding 10%, oxygen deficiency is not formed, and the film forming speed cannot be increased. On the other hand, if the oxygen partial pressure is less than 1%, the rate of crystals parallel to the axis of polarization is lowered, and piezoelectric characteristic is not improved. That is, to obtain a necessary piezoelectric characteristic, the crystal orientation degree of 70% or more is required, and the oxygen partial pressure is required to be more than 1% for this purpose. By sputtering at a relatively low oxygen partial pressure, the film forming rate is higher and the mass producibility is improved.

[0094] In the sputtering method or laser ablation method, the gas feed flow rate into the vacuum apparatus may be 0.01 or more to less than 0.1 as the ratio of the oxygen gas feed flow rate to the total gas feed flow rate. As a result, in the discharge gas pressure condition of relatively low pressure, an oxide piezoelectric thin film of specified oxygen deficiency ratio can be obtained, and film forming at high speed is realized, and the mass producibility is much enhanced. 

What is claimed is:
 1. A piezoelectric device comprising: a first electrode film; a second electrode film; and a piezoelectric thin film enclosed by the first electrode film and the second electrode film, wherein the piezoelectric thin film is an oxide piezoelectric thin film having an oxygen deficiency amount of more than 0% and not more than 10% of the stoichiometric composition.
 2. The piezoelectric device of claim 1, wherein the piezoelectric thin film is a lead zirconic titanate expressed in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z) (where 0<X<1), and a ratio of oxygen deficiency amount in the piezoelectric thin film expressed as (Y−Z)/(Y+3) is in a range of 0<(Y−Z)/(Y+3)≦0.1.
 3. The piezoelectric device of claim 2, wherein the piezoelectric thin film is 70% or more in a crystal orientation degree of an azimuth parallel to an axis of polarization.
 4. The piezoelectric device of claim 2, wherein the piezoelectric thin film has a crystal structure of perovskite tetragonal system, and a crystal orientation oriented in (001) direction.
 5. The piezoelectric device of claim 2, wherein the piezoelectric thin film has a crystal structure of perovskite rhombohedral system, and a crystal orientation oriented in (111) direction.
 6. The piezoelectric device of claim 2, wherein a part of Pb in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z) (where 0<X<1) is replaced by at least one element selected from the group consisting of group 2 elements of manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), samarium (Sm), europium (Eu) and ytterbium (Yb).
 7. The piezoelectric device of claim 2, wherein a part of at least one element selected from Ti and Zr in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z) (where 0<X<1) is replaced by at least one element selected from the group consisting of hafnium (Hf), iridium (Ir), silicon (Si), germanium (Ge), tin (Sn), cerium (Ce), praseodymium (Pr) and terbium (Tb).
 8. The piezoelectric device of claim 2, wherein a part of at least one element selected from Pb, Ti and Zr in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z) (where 0<X<1) is replaced by at least one element selected from the group consisting of group 1 elements of valence of 1, that is, scandium (Sc), yttrium (Y), chromium (Cr), boron (B), aluminum (Al), gallium (Ga), indium (In), antimony (Sb), bismuth (Bi), lanthanum (La), neodymium (Nd), promethium (Pm), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm) and lutetium (Lu).
 9. The piezoelectric device of claim 1, wherein the piezoelectric thin film is manufactured by a sputtering method or a laser ablation method.
 10. A method of manufacturing a piezoelectric device comprising: forming a first electrode film on a substrate; forming an oxide piezoelectric thin film expressed in general formula A_(1+Y)BO_(3+Z) (where A and B represent elements) and 70% or more in a crystal orientation degree of an azimuth parallel to an axis of its polarization, on the first electrode film, by a sputtering method or a laser ablation method, at an oxygen partial pressure in a vacuum apparatus during film forming process in a range of 1% or more to less than 10% of a total pressure; forming a second electrode film on the oxide piezoelectric thin film; and processing the first electrode film, the oxide piezoelectric thin film and the second electrode film so as to form a pattern shape.
 11. The method of manufacturing the piezoelectric device of claim 10, wherein the oxide piezoelectric thin film is a lead zirconic titanate expressed in general formula A_(1+Y)BO_(3+Z) (where A and B represent elements) where A is lead (Pb), and B is zirconium (Zr) and titanium (Ti), its crystal structure is perovskite tetragonal system, and its crystal orientation is oriented in (001) direction.
 12. The method of manufacturing the piezoelectric device of claim 10, wherein the oxide piezoelectric thin film is a lead zirconic titanate expressed in general formula A_(1+Y)BO_(3+Z) (where A and B represent elements) where A is lead (Pb), and B is zirconium (Zr) and titanium (Ti), its crystal structure is perovskite rhombohedral system, and its crystal orientation is oriented in (111) direction.
 13. The method of manufacturing the piezoelectric device of claim 10, wherein a target composition of film forming source in the sputtering method or the laser ablation method is specified by 0<Y<1 and −3≦Z≦Y in general formula Pb_(1+Y)(Zr_(X)Ti_(1−X))O_(3+Z) (where 0<X<1).
 14. The method of manufacturing the piezoelectric device of claim 10, wherein as a gas feed flow rate into the vacuum apparatus in the sputtering method or the laser ablation method, a ratio of a oxygen gas feed flow rate to a total gas feed flow rate is 0.01 or more to less than 0.1. 